EP4279705A1

EP4279705A1 - Double layer wear and corrosion protected shank adapter

Info

Publication number: EP4279705A1
Application number: EP22174656.3A
Authority: EP
Inventors: Thomas BLOMFELDT; Marcus Anerud; Johan Portin; Benneth LEANDERS
Original assignee: Sandvik Mining and Construction Tools AB
Current assignee: Sandvik Mining and Construction Tools AB
Priority date: 2022-05-20
Filing date: 2022-05-20
Publication date: 2023-11-22

Abstract

A shank adapter to form part of a drilling assembly, the shank adapter comprising a longitudinal axis; an external surface; an internal surface; a threaded part provided at a forward end and a plurality of splines provided at a rearward end; and a machine part extending axially between the threaded part and the splines; characterised in that: at least a part of the external surface is coated with a first corrosion protection layer comprising chromium and a second corrosion protection layer.

Description

Field of invention

The present invention relates to a shank adapter for top hammer rock drilling having a corrosion and / or wear protection layer.

Background

Shank adapters are used in rock drills as the main component which transfers the impact energy from the piston to the drill string while being rotated. Further, shank adapters are used to transfer flushing media from the rock drill into the drill string. Since shank adapters need to have high impact resistance, they are typically made from high strength carburized steel. However, the drawback of this material is that it is corroded by the flushing media, which may for example contain chloride, sulphide or other ions which accelerate the corrosion. If the shank adapter is corroded, its functionality decreases. The steel may for example have issues with stress corrosion cracking as the mechanical strength of the material is decreased.
Further, it is important to maintain the integrity of the seals inside the flushing housing for preventing leakage of the flushing water and maintaining good flushing pressure. For the seals to not wear out prematurely, it is important that the surface of the shank adapter in contact with the seals remains in a good, non-corroded condition. A corroded surface is highly abrasive and leads to premature failure of the seals in the flushing housing of the rock drill.
Therefore, it is advantageous to provide a corrosion protection coating on the surface of the shank adapter.
A known method of corrosion protection on shank adapters is to provide a single layer of hard chrome plating on its surface. However, the hard chrome layers contain pores and microcracks which can act as channels for the water to penetrate through and reach the surface of the shank adapter therefore removing the corrosion protection. Therefore, the problem to be solved is how to improve the corrosion and / or wear resistance of surfaces of the shank adapter.

Summary of the Invention

It is an objective of the present invention to provide an alternative means to increase the corrosion and / or wear resistance of shank adapters. This objective is achieved by providing a shank adapter to form part of a drilling assembly, the shank adapter comprising: a longitudinal axis; an external surface; an internal surface; a threaded part provided at a forward end and a plurality of splines provided at a rearward end; and a machine part extending axially between the threaded part and the splines; characterised in that at least a part of the external surface is coated with a first corrosion protection layer comprising chromium and a second corrosion protection layer.
Advantageously, the combination of the first and second corrosion protection layers provides increased corrosion protection.
In one embodiment, the thickness of first corrosion protection layer is between 5-200 µm. Advantageously, this thickness provides the optimal balance between providing sufficient corrosion protection without adding excessive costs.
In one embodiment, the second corrosion protection layer comprises chromium. Advantageously, the double chrome layer reduces the amount of uncontrolled micro fractures acting as channels to the steel substrate which are formed during the chromium coating process. This is done by first applying a first chrome layer on the shank adapter. This first chrome layer is thereafter polished before the second chrome layer is applied on top of the first. This results that an "interface" being is formed between the first and second layer which prevents the cracks to run through the entire layers, resulting in that less water can penetrate through the layer.
In one embodiment, the thickness of second corrosion protection layer is is between 5 - 200 µm. Advantageously, this thickness provides the optimal balance between providing sufficient corrosion protection without adding excessive costs or the layer becoming so thick that it becomes unstable from the additional internal stresses within the layer that is built up.
In one embodiment, the shank adapter further comprises a third corrosion protection layer comprising chromium. Advantageously, this further reduces the level of uncontrolled micro fractures acting as channels to the steel substrate which are formed during the chromium coating process.
In one embodiment, the second corrosion protection layer is a laser cladding layer. Advantageously, the laser cladded layer would add a cost-efficient wear and corrosion protective layer. Laser cladding is a fast which is advantageous for production and produces a more reliable corrosion protection layer which will increase the lifetime of the shank adapter and other drilling components that attach to the shank adapter.
In one embodiment, the heat effected zone extends < 0.3 mm into a substrate. Advantageously, the reduction in the depth of the heat effected zone provides an increase in the wear resistance of the laser cladding layer.
In one embodiment, the second corrosion protection layer is a nickel phosphorus alloy plating and a fluoroplastic layer. Advantageously, the combination provides improved wear and corrosion resistance.
In one embodiment, the second corrosion protection layer comprises nickel. Advantageously, the combination of the nickel and chromium corrosion protection layers provides increased resistance against corrosion and wear.
In one embodiment, the first corrosion protection layer and the second corrosion protection layer are located on the machine part. Advantageously, this provides corrosion protection to the region of the shank adapter that is most exposed to corrosion and most important to be protected from corrosion.
In one embodiment, the first corrosion protection layer is located between the external surface of the shank adapter and the second corrosion protection layer.
In one embodiment, the shank adapter further comprises a layer of phosphate between the external surface and the first corrosion protection layer. Advantageously, this adds additional corrosion protection.
According to another aspect of the present invention is a method of providing corrosion protection on a shank adapter as described hereinbefore or hereinafter comprising the step of:

a) depositing the first corrosion protection layer comprising chromium on at least part of the external surface of the shank adapter;
b) depositing the second corrosion protection layer on at least part of the external surface of the shank adapter;

Advantageously, this produces a shank adapter having increased corrosion protection.
In one embodiment of the method, the addition of the second corrosion protection layer is selected from chromium plating, laser cladding or deposition of a nickel phosphorus alloy plating with or without a fluoroplastic layer.
In one embodiment of the method the second corrosion protection layer is deposited using extreme high-speed laser application (EHLA). Advantageously, EHLA provides thinner layers, with a reduced heat effected zone as the dilution between the cladding and the substrate is smaller, with higher power efficiency and faster processing times.

Brief description of drawings

A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

Figure 1 is a schematic drawing of a shank adapter.
Figure 2 is a schematic drawing of one embodiment of the corrosion protection layer.
Figure 3 is a schematic drawing of a further embodiment of the corrosion protection layer.

Detailed description

Figure 1 shows a shank adapter 2 to form part of a drilling assembly, the shank adapter 2 comprising, a longitudinal axis 4; an external surface 6; an internal surface 8; a threaded part 10 provided at a forward end 12 and a plurality of splines 32 that project radially outward provided at a rearward end 14; and a machine part 16 (otherwise known as a main body) extending axially between the threaded part 10 and the splines 32. The splines 32 are configured to be engaged by corresponding splines of a drive bushing in a rotational motor (not shown) to induce rotation of the shank adaptor 2 about axis 4 during drilling operations. The threaded part 10 could be either a male or female thread. The shank adapter further comprises a flushing hole 26 (or bore) located on the machine part 16 that extends radially through the machine part 16 from the external surface 6 to an internal cavity or region extending axially within the shank adaptor 2. The shank adaptor 2 is configured for coupling to an elongate drill string and to allow transmission of a stress wave to a drill bit (not shown) located at the deepest region of the drill hole to impart the percussion drilling action. In particular, the forward end 12 may be coupled to a rearward end of a rearwardmost elongate drill rod forming a part of the drill string or to a coupling (not shown). The rearward end 14, otherwise known as the striking face, is configured to be contacted by a hydraulically driven piston (not shown) that creates the stress wave within the shank adaptor 2 and the drill string. Optionally the forward end 12 also comprises an annular shoulder 28 from which the threaded part 10 axially projects. Optionally, a slim 30 is positioned axially between the machine part 16 and the threaded part 10.
Figure 2 shows that at least a part of the external surface 6 is coated with a first corrosion protection layer 18 comprising chromium and a second corrosion protection layer 20.
In one embodiment the thickness of first corrosion protection layer 18 is between 5-200 µm, more preferably between 7-100 µm, even more preferably between 10-50 µm.
In one embodiment, the second corrosion protection layer 20 comprises chromium.
In one embodiment, when the second corrosion protection layer 20 comprises chromium, the thickness of second corrosion protection layer 20 is between 5-200 µm, more preferably between 7-100 µm, even more preferably between 10-50 µm.
Figure 3 shows an alternative embodiment wherein the shank adapter 2 further comprises a third corrosion protection layer 22 comprising of chromium positioned on top of the second corrosion protection layer 20.
In one embodiment, when the thickness of third corrosion protection layer 22 is between 5-200 µm, more preferably between 7-100 µm, even more preferably between 10-50 µm.
In another embodiment, the second corrosion protection layer 20 is a laser cladding layer.
In one embodiment, when the second corrosion protection layer 20 is laser cladding, preferably the thickness second corrosion protection layer 20 is between 10 - 2000 µm, preferably between 10 - 800 µm, more preferably 20 - 200 µm. Preferably, the laser cladding layer(s) is /are applied such that the outer diameter of the section of the shank adapter 2 where the laser cladding layer(s) has been applied is substantially uniform.
In one embodiment, the composition of the laser cladding layer comprises a metal matrix composite (MMC). The MMC comprises a hard metal for example this could be tungsten carbide, chromium carbide, titanium carbide, tantalum carbide, niobium carbide or any other carbide or nitride or a mixture thereof and a metal alloy as a binder which could for example comprise cobalt, nickel, iron, chromium or a mixture thereof. Advantageously, the presence of the metal matrix composite increases the wear resistance of the laser cladding.
Alternatively, the composition of the laser cladding corrosion protection layer comprises a metal alloy. The composition of the laser cladding material could be stainless steel or tool steel. The composition of the laser cladding material could for example be pure nickel, a nickel-based alloy e.g. a Ni-Cr alloy; an Fe based alloy; a Cr-based alloy; a mixture thereof or any other suitable material. The material selected can be chosen to suit the specific application and drilling environment, for example stainless steel will provide better corrosion protection, whereas tool steel or hard metal composite will provide better wear resistance. Advantageously, the metal alloy can be selected having superior corrosion and /or wear resistance to suit the application.
Preferably, the laser cladding has a hardness of between 180 to 1500 HV10, more preferably 400-1400 HV10 , even more preferably 500-1300 HV10. Preferably, the coating is dense enough to prevent water from reaching the external surface 6 of the machine part 16. Hardness measurements are an average value for the cladded layer.
If the cladding layer is an MMC preferably the hardness of the metal matrix is 500-900 HV10, preferably 600-900 HV10, more preferably 600-900 HV10 and the hardness of the hard metal phase is 1500-3500 HV0.1, preferably 2000-3500 HV0.1 and most preferably 2500-3500 HV0.1. Advantageously, this provides increased wear resistance.
In one embodiment the heat effected zone extends < 0.3 mm into the substrate, preferably < 0.2 mm, more preferably less than 0.1 mm. The heat effected zone is defined as being the area of heat altered substrate material between the applied coating and the unaffected substrate.
The substrate is the surface that the laser cladding layer is applied to, therefore is most likely to be the chromium of the first corrosion protection layer 18 but could also be the steel of the external surface 6 of the shank adapter 2.
In one embodiment, the second corrosion protection layer 20 comprises nickel.
In one embodiment, additionally at least part of the internal surface is coated with a first corrosion protection layer comprising nickel.
Optionally, the nickel is alloyed with sulphur, phosphorus, boron or any other suitable element.
In one embodiment, the second corrosion protection layer 20 is a nickel phosphorus alloy plating and a fluoroplastic layer. For example a Nedox coating could be used. Preferably, the thickness of the nickel phosphorus alloy plating and a fluoroplastic layer is between 10 - 50 µm.
Preferably, the nickel phosphorus alloy plating and a fluoroplastic layer is positioned on top of the chromium layer.
Optionally, at least part of the internal surface 8 is additionally coated with a first corrosion protection layer 18 comprising nickel.
In one embodiment the first corrosion protection layer 18 is located on the machine part 16. In other words, the first corrosion protection layer 18 is not positioned on the splines 32 or the threaded part 10. Alternatively, the entire external surface 6 of the shank adapter 2 is coated with a first corrosion protection layer 18.
In one embodiment, the laser cladding layer(s) is / are positioned around the flush hole 26 that extends radially and longitudinally through the machine part 16. Advantageously, this provides corrosion / wear protection in the region that is most subjected to corrosive attack and wear.
In one embodiment, the second corrosion protection layer 20 is present in all areas on the external surface 6 of the shank adapter 2 where the first corrosion protection 18 is located.
For example, this is most likely to be the machine part 16. Advantageously, this will provide optimal corrosion protection.
In another embodiment, one or more areas of the external surface 6 of the shank adapter 2 are coated with both the first corrosion protection layer 18 and the second corrosion protection layer 20 and one or more areas of the external surface 6 of the shank adapter are coated with only the first corrosion protection layer 18 or only the second corrosion protection layer 20.
Preferably, the first corrosion protection layer 18 is located between the external surface 6 of the shank adapter 2 and the second corrosion protection layer 20 as shown in figure 3. Alternatively, the second corrosion protection layer 20 is located between the external surface 6 of the shank adapter 2 and the first corrosion protection layer 18.
Another aspect of the present application relates to a method of providing corrosion protection on a shank adapter 2 comprising the step of:

a) depositing the first corrosion protection layer 18 comprising chromium on at least part of the external surface 6 of the shank adapter 2;
b) depositing the second corrosion protection layer 20 on at least part of the external surface 6 of the shank adapter 2;

In one embodiment, the chromium of the first corrosion protection layer 18 is applied using electroplating.
The second corrosion protection layer 20 is selected from chromium plating, laser cladding or deposition of a nickel phosphorus alloy plating and a fluoroplastic layer.
In one embodiment, if the second corrosion protection layer 20 is nickel it can be applied using an electroless nickel bath or using electroplating . In electroless nickel plating, the object instead reacts to the plating bath chemistry, creating a uniform and smooth, layer with very little surface porosity. The even deposition makes it an ideal choice for complex, non-line of sight, geometries and often eliminates grinding after plating. The nickel plating is applied to improve the corrosion and wear resistance of an object. Alternatively, the nickel layer could be added using a laser cladding method, for example EHLA laser cladding.
Preferably the first corrosion protection layer 18 is added before the second corrosion protection layer 20. In other words, the second corrosion protection layer 20 is added on top of the first corrosion protection layer 18, but it could be the other way around.
In one embodiment, where the second corrosion protection layer 20 is a laser cladding layer. Laser cladding is a melting process where a laser beam is used to fuse a powder alloy with another metallurgical composition onto a substrate. A metallic substrate is exposed to a laser beam while a powder is injected over the melted bath to form, after being solidified, a layer referred to as the cladding on the surface of the substrate. The key benefit is that only a very thin layer of the substrate has to be melted in order to achieve a metallurgical bond between the added material and the substrate. The laser cladding could be applied using a fiber, C02, YAG or diode laser or any other suitable laser.
Preferably, the laser cladding is done using extreme high-speed laser material deposition (EHLA). EHLA is a laser cladding method which is up to 10 times faster than traditional laser cladding methods in terms of surface coverage rate. The high-speed deposition from EHLA does not only result in a faster processing time, it also makes it possible to apply cladding to a substrate with even lower heat input and smaller distortion, meaning that the heat effected zone will be even less in the substrate. In addition, the small dilution formed by EHLA makes it possible to apply even thinner coatings, the thickness of the laser cladding layers is for example typically only 25-400 µm thick. Advantageously, this inputs less energy into the substrate that the laser cladding is applied to, resulting in reduced substate melting, therefore the wear and corrosion resistance of the substrate is maintained. EHLA provides thinner layers, with a reduced heat effected zone as the dilution between the cladding and the substrate is smaller, with higher power efficiency and faster processing times.
Preferably, the surface that the laser cladding layer is applied to is ground and / or polished prior to application of the laser cladding layer(s). Advantageously, this increases the adhesion of the laser cladding corrosion protection layer to the external surface of the shank adapter. Alternatively, the surface that the laser cladding layer is applied to may be left unground, which has the advantage of quick processing time. Additionally, or alternatively, surface that the laser cladding layer is applied to could be carburized and / or pre-heated prior to laser cladding.
Preferably, the outermost laser cladding layer is ground and / or polished. Advantageously, this reduces wear on the seals and therefore the lifetime of the product is increased and may reduce the area where possible cracks can be initiated from. Alternatively, the surface could be left unprocessed, which has the advantage of decreasing processing time.
Preferably, the laser cladding step is done after the application of the first corrosion protection. However, the steps could be done in any order as desired.
In one embodiment the method further comprising the step of applying fluoroplastic layer. For example, the fluoroplastic layer could be applied using a spraying technique, following by a heat treatment for curing.
In one embodiment, the shank adapter further comprising a layer of phosphate between the external surface 6 and the first corrosion protection layer 18. For example, the phosphate layer could be selected from, but not limited to zinc phosphate, zinc manganese phosphate, or manganese phosphate.
The shank adapter as described hereinbefore or hereinafter could be part of a drill string and / or a drill rig arrangement.

Examples

Example 2 - Lab based corrosion test

Corrosion testing was performed on samples cut from a chromed machine part of the shank adapter, nearest the thread. Salt and acetic acid solution was sprayed on the samples and examined after different time intervals. Prior to each check, the samples were rinsed in water and excess corrosion products were washed off. The sample was then examined under a bright spot light to create a bright reflective band on the curved surface and when a defect passed the reflective band the buckling could be seen in the reflective band since it would deflect the light and the defect was marked with black pen. The chromed surface was examined over the entire circumference and the number of defects were counted per sample. After the investigation the samples were put back in a plastic container and sprayed with the acetic acid and NaCl solution from all sides and left under a lid until the next examination a few days later. The results are shown in table 1 below:

Table 1: Number of defects observed on chrome plated surface

Sample	A (comparative)	B (invention)	C (invention)
Coating	Single chromium layer - 50 µm thick	Double chromium layer - both layers 25 µm thick	Double chromium layer - both layers 40 µm thick
0 days	0	0	0
1 day	0	0	0
10 days	4	0	0
19 days	50	2	0

It can be seen that the inventive samples have significantly less defects post the corrosion testing, therefore demonstrating their superior corrosion resistance.

Example 2 - Field trial

Shank adapters with different corrosion protection layers were tested at Kristinebergsgruvan a Boliden mine in Sweden. All samples were drilling until they were worn out and discarded. After drilling the shank adapters were visually inspected and the degree of corrosion was judged on scale of 1-5 (1 = least corrosion and 5 = worst corrosion) based on their resistance to pitting and crevicing. The results are shown in table 2 below:

Table 2: Visual inspection of shank adapters post drilling

Shank adapter sample	Corrosion protection coating	Pitting on chrome surface	Crevice corrosion or wear on chromed surface
A (comparison)	Single chromium layer - 50 µm thick	5	5
B (invention)	Double chromium layer - both layers 25 µm thick	3	4
C (invention)	Double chromium layer - both layers 40 µm thick	1	3

It can be seen that there was a reduction in both pitting and crevice corrosion for the invention samples compared to a single layer on chromium.

Claims

A shank adapter (2) to form part of a drilling assembly, the shank adapter (2) comprising:
a longitudinal axis (4);

an external surface (6);

an internal surface (8);

a threaded part (10) provided at a forward end (12) and a plurality of splines (32) provided at a rearward end (14); and

a machine part (16) extending axially between the threaded part (10) and the splines (32);
characterised in that:
at least a part of the external surface (6) is coated with a first corrosion protection layer (18) comprising chromium and a second corrosion protection layer (20).
The shank adapter (2) according to claim 1, wherein the thickness of first corrosion protection layer (18) is between 5-200 µm.
The shank adapter (2) according to claim 1 or claim 2, wherein the second corrosion protection layer (20) comprises chromium.
The shank adapter (2) according to claim 3 wherein the thickness of second corrosion protection layer (20) is is between 5 - 200 µm.
The shank adapter (2) according to any of the previous claims, further comprising a third corrosion protection layer (22) comprising chromium.
The shank adapter according to claim 1 or claim 2 wherein the second corrosion protection layer (20) is a laser cladding layer.
The shank adapter according to any of the previous claims wherein the heat effected zone extends < 0.3 mm into a substrate (6, 18).
The shank adapter according to claim 1 or 2 wherein the second corrosion protection layer (20) comprises Ni.
The shank adapter according to claim 8 wherein the second corrosion protection layer (20) is a nickel phosphorus alloy plating and a fluoroplastic layer.
The shank adapter (2) according to any of the previous claims wherein the first corrosion protection layer (18) and the second corrosion protection layer (20) are located on the machine part (16).
The shank adapter (2) according to any of the previous claims wherein the first corrosion protection layer (18) is located between the external surface (6) of the shank adapter (2) and the second corrosion protection layer (20).
The shank adapter (2) according to any of the previous claims further comprising a layer of phosphate between the external surface (6) and the first corrosion protection layer (18).
A method of providing corrosion protection on a shank adapter (2) according to any of claims 1-12 comprising the step of:
a) depositing the first corrosion protection layer (18) comprising chromium on at least part of the external surface (6) of the shank adapter (2);

b) depositing the second corrosion protection layer (18) on at least part of the external surface (6) of the shank adapter (2);
wherein the step a) or b) could be performed first.
The method according to claim 13 wherein the second corrosion protection layer is selected from chromium plating, laser cladding or deposition of a nickel phosphorus alloy plating and a fluoroplastic layer.
The method according to claim 13 or 14 wherein the second corrosion protection layer (20) is deposited using extreme high-speed laser application (EHLA).